Bacteroides is one of the major genera in the human colonic microflora. Polysaccharides, either from the diet or host secretions, are probably the natural substrates for many of these obligately saccharolytic bacteria. Polysaccharide utilization in vivo will be affected by factors such as slow growth rates, low concentrations of available polysaccharides, the complexity of this mixture and the covalent linkage of polysaccharides to proteins or other substances in natural aggregates (e.g. plant cell walls or tissue glycoproteins). Moreover, most polysaccharide-degrading enzymes produced by Bacteroides are not extracellular and outer membrane receptors appear to be important for polysaccharide utilization. The objective of this proposal is to use model systems to investigate mechanisms of polysaccharide utilization by Bacteroides and to study some of the factors which affect this process. Polysaccharides will include tissue mucopolysaccharides, as well as plant cell wall polysaccharides. For most of these studies, B. thetaiotamicron will be used as a typical polysaccharide degrader. Topics to be investigated include (a) characterization of outer membrane receptors for polysaccharides, (b) affinity of bacteria for different polysaccharides and the effect of naturally occuring membrane active compounds (bile, acids, phytic acid) on affinity, (c) utilization of mixtures of polysaccharides, (d) utilization of proteoglycan, a well-characterized aggregate containing mucopolysaccharides and protein, and (e) of guar gum (a plant galactomannan) by Bacteroides, one of the few known cases in which an extracellular polysaccharidase may be produced.